The present invention is related to an actuator for manipulating a controlled object in accordance with an axial position of a control shaft while transferring a rotation of a motor to a reciprocating motion of the control shaft, and a valve lift control system using the actuator.    1. Related Art
In an automotive engine, an actuator is used for manipulating a controlled object in accordance with an axial position of a control shaft.
According to a variable valve mechanism for an internal combustion engine in U.S. Pat. No. 6,425,357 (JP-A-2001-263015), an intermediate driving mechanism is movably supported on its axis independent of the axis of a valve cam. The intermediate driving mechanism includes a control shaft, a valve cam related part and intake valve related parts. The intermediate driving mechanism is provided for transmitting a driving force of the valve cam to an intake valve. A reciprocating motion of the control shaft is transferred into a rotation motion of the valve cam related part and a rotation motion of the intake valve related parts. Accordingly, the relative lift-difference of the valve cam related part with the intake valve related parts are controlled based on the axial position of the control shaft. Here, controlled object can be an exhaust valve instead of the intake valve.
However, the axial position of the control shaft is controlled by adjusting oil pressure in a pressure chamber. The pressure chamber is provided on one end side of the control shaft for reciprocating the control shaft. In this structure, a piston for receiving oil pressure from the pressure chamber and a housing for forming a pressure chamber are provided so as to control differential pressure between the front side of the piston and the rear side of the piston. Accordingly, controllability of a position and response is inferior.
Here, an electric actuator can be used instead of a hydraulic actuator. However, a length of the electric actuator may be elongated in the axial direction of the control shaft depending on an arrangement of a motor and the control shaft.